The present invention is generally related to nanostructures and, more particularly, is related to nanowires and nanospheres and methods for their preparation and use.
Semiconductor nanostructures, nanoagglomerates, and nanowires have attracted considerable attention because of their potential applications in mesoscopic research, the development of nanodevices, and the potential application of large surface area structures. For several decades, the vapor-liquid-solid (VLS) process, where gold particles act as a mediating solvent on a silicon substrate forming a molten alloy, has been applied to the generation of silicon whiskers. The diameter of the whisker is established by the diameter of the liquid alloy droplet at its tip. The VLS reaction generally leads to the growth of silicon whiskers epitaxially in the  less than 111 greater than  direction on single crystal silicon  less than 111 greater than  substrates. In addition, laser ablation techniques have been performed on metal-containing (iron or gold) silicon targets, producing bulk quantities of silicon nanowires. Further, thermal techniques have been used to produce a jumble of silicon dioxide (SiO2) coated crystalline nanowires that have their axes parallel to the  less than 112 greater than  direction. Further, these nanowires are deficient because of twinning, high order grain boundaries, and stacking faults.
Recently, national lab researchers, in an effort to begin an ongoing dialogue to forecast the direction of environmental science and technology, ranked the top ten environmental technology breakthroughs for 2008. Not surprisingly, molecular design is expected to play an important role in the development of advanced materials. Included in this framework is the design of nano-assembled and non-stoichiometric catalysts designed for the efficient control of chemical processes.
Heterogeneous catalysts are typically prepared by decorating high surface area solids such as silica or alumina with active metals or metal ions from precursor materials such as cation complexes [Mn+(Lmxe2x88x92X](nxe2x88x92xm), anion complexes (e.g., [Pt4+F6]2xe2x88x92 or neutrals such as copper (II) acetylacetonate (Cu(AcAc)2)). These processes typically use starting reagents and produce products that are harmful to the environment (e.g. solvents, metal halides, strong acids, or other environmentally aggressive reagents and or products). A high-surface-area support is needed to provide the proper dispersion of the active ingredients so that the high intrinsic activity of these catalytic metals or ions can be realized in practice. Without this support, many catalytic agents show very little active surface area. Often, the intrinsic catalytic activity of the supported metals or metal ions is changed by interaction with the support metal ions or oxygen atoms. Thus, some supports are not benign towards the catalytic agents. Moreover, the catalytic properties of these agents are often compromised as a result of the efforts to synthesize supported catalysts having high dispersions of the active ingredient. These uniquely assembled catalysts might then be used to more efficiently control combustion processes, and reactions such as hydrocarbon reforming.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
An embodiment of the present invention provides for a nanowire and method of fabrication thereof. The method includes fabricating the nanowires under thermal and non-catalytic conditions. The nanowires can be fabricated from at least metals, metal oxides, metalloids, and metalloid oxides. A preferred embodiment of the present invention includes, but is not limited to, the fabrication of a silicon dioxide sheathed crystalline silicon nanowire, where the axis of the crystalline silicon nanowire core is substantially parallel to a  less than 111 greater than  plane and is substantially free of defects.
Another embodiment of the present invention provides for a nanosphere and method of fabrication thereof. The method includes fabricating the substantially monodisperse nanospheres under thermal and non-catalytic conditions. The nanospheres can at least be fabricated from metals, metal oxides, metalloids, and metalloid oxides. A preferred embodiment of the present invention includes, but is not limited to, fabricating amorphous silicon dioxide nanospheres.
Still another embodiment of the present invention provides for a metallized nanosphere and method of fabrication thereof. The method includes fabricating the subtantially monodisperse nanospheres under thermal and non-catalytic conditions. The nanospheres can be fabricated from at least metals, metal oxides, metalloids, and metalloid oxides. The nanospheres can be metallized to form metallized nanospheres that are capable of having catalytic properties. In addition, the formation of the nanospheres and metallization of the nanospheres can be performed substantially in one step. A preferred embodiment of the present invention includes fabricating amorphous silicon dioxide nanospheres and depositing three weight percent (%) copper onto the nanosphere.
Still a further embodiment of the present invention provides for a method of the dehydrogenation of ethanol. The method includes introducing gaseous ethanol to three weight percent metallized silicon dioxide nanospheres to produce at least a three percent conversion/mg copper for the selective dehydrogenation of ethanol into acetaldehyde.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.